Endothelial-Mesenchymal Transition:miR-101 as a new target to treat intimal hyperplasia

Introduction: Endothelial-Mesenchymal Transition (EndMT) is a specific form of endothelial dysfunction wherein endothelial cells acquire a mesenchymal phenotype and lose their endothelial functions. We, and others, recently described that EndMT contributes to intimal hyperplasia and atherosclerosis. Pro-fibrotic and inflammatory cytokines, such as IL-1β and TGFβ2 induce EndMT. We found that the mitogen activated protein kinase 7 (MAPK7, also known as Erk5) inhibits EndMT. MAPK7 activation decreases the expression of the histone methyltransferase Enhancer-of-Zeste homologue 2 (Ezh2) thereby maintaining endothelial quiescence.This decrease in Ezh2 expression may therefore be responsible for the protective effects of MAPK7 activation and may thus offer new therapeutic options for the treatment of endothelial dysfunction and intimal hyperplasia. Ezh2 is the catalytic subunit of the Polycomb Repressive Complex 2 that methylates lysine 27 on histone 3 (H3K27me3). H3K27me3 is a repressive chromatin mark that inhibits gene expression. Currently, it is elusive how the crosstalk between MAPK7 and Ezh2 is regulated in the endothelium and if the balance between MAPK7 and EZH2 is disturbed during intimal hyperplasia. Methods and results: We used in silico analysis to identify miRNAs that could evoke posttranscriptional silencing of Ezh2. In Luciferase reporter assays, miR-101 efficiently inhibited expression of the luciferase reporter by interacting with the 3’UTR of EZH2. Using a uniform laminar flow setup, we revealed that MAPK7 induced miR-101 expression, which was blocked by the selective MAPK7 inhibitor BIX02189 (p<0.05). Furthermore, ectopic expression of miR-101 in endothelial cells reduced the expression of Ezh2. In samples of human coronary artery stenosis Ezh2 levels are increased, whereas MAPK7 expression is reduced. Moreover, miR-101 expression is decreased, which associated with the increase of Ezh2 (R2=0.23, p=0.051) and severity of the stenosis (Intima/Media Thickness, R2=0.45, p=0.003). Conclusion(s): Under uniform laminar flow MAPK7 inhibits Ezh2 expression via activation of miR-101. In coronary artery stenosis, endothelial cells are exposed by non-uniform shear stress which decreases MAPK7 activation, miR-101 expression and concurrently increases Ezh2 expression, which may cause EndMT and intimal hyperplasia. Therefore, the restoration of miR-101 expression or the silencing of Ezh2 in the endothelium might provide novel therapeutic approaches to treat intimal hyperplasia

Histone deacetylase inhibitors exert anti-tumor effects on human adherent and stem-like glioma cells 11 Medical and Health Sciences 1112 Oncology and Carcinogenesis

Background: The diagnosis of glioblastoma (GBM), a most aggressive primary brain tumor with a median survival of 14.6 months, carries a dismal prognosis. GBMs are characterized by numerous genetic and epigenetic alterations, affecting patient survival and treatment response. Epigenetic mechanisms are deregulated in GBM as a result of aberrant expression/activity of epigenetic enzymes, including histone deacetylases (HDAC) which remove acetyl groups from histones regulating chromatin accessibility. Nevertheless, the impact of class/isoform-selective HDAC inhibitors (HDACi) on glioma cells, including glioma stem cells, had not been systematically determined. Results: Comprehensive analysis of the public TCGA dataset revealed the increased expression of HDAC 1, 2, 3, and 7 in malignant gliomas. Knockdown of HDAC 1 and 2 in human GBM cells significantly decreased cell proliferation. We tested the activity of 2 new and 3 previously described HDACi with different class/isoform selectivity on human GBM cells. All tested compounds exerted antiproliferative properties on glioma cells. However, the HDACi 1 and 4 blocked proliferation of glioblastoma cells leading to G2/M growth arrest without affecting astrocyte survival. Moreover, 1 and 4 at low micromolar concentrations displayed cytotoxic and antiproliferative effects on sphere cultures enriched in glioma stem cells. Conclusions: We identified two selective HDAC inhibitors that blocked proliferation of glioblastoma cells, but did not affect astrocyte survival. These new and highly effective inhibitors should be considered as promising candidates for further investigation in preclinical GBM models

Hypoxia promotes osteogenesis by facilitating acetyl-CoA-mediated mitochondrial-nuclear communication

Bone-derived mesenchymal stem cells (MSCs) reside in a hypoxic niche that maintains their differentiation potential. While hypoxia (low oxygen concentration) was reported to critically support stem cell function and osteogenesis, the molecular events triggering changes in stem cell fate decisions in response to normoxia (high oxygen concentration) remain elusive. Here, we study the impact of normoxia on mitochondrial-nuclear communication during stem cell differentiation. We show that normoxia-cultured murine MSCs undergo profound transcriptional alterations which cause irreversible osteogenesis defects. Mechanistically, high oxygen promotes chromatin compaction and histone hypo-acetylation, particularly on promoters and enhancers of osteogenic genes. Although normoxia induces metabolic rewiring resulting in elevated acetyl-CoA levels, histone hypo-acetylation occurs due to the trapping of acetyl-CoA inside mitochondria owing to decreased citrate carrier (CiC) activity. Restoring the cytosolic acetyl-CoA pool remodels the chromatin landscape and rescues the osteogenic defects. Collectively, our results demonstrate that the metabolism-chromatin-osteogenesis axis is perturbed upon exposure to high oxygen levels and identifies CiC as a novel, oxygen-sensitive regulator of the MSC function

Chromatin remodeling due to degradation of citrate carrier impairs osteogenesis of aged mesenchymal stem cells

Aging is accompanied by a general decline in the function of many cellular pathways. However, whether these are causally or functionally interconnected remains elusive. Here, we study the effect of mitochondrial–nuclear communication on stem cell aging. We show that aged mesenchymal stem cells exhibit reduced chromatin accessibility and lower histone acetylation, particularly on promoters and enhancers of osteogenic genes. The reduced histone acetylation is due to impaired export of mitochondrial acetyl-CoA, owing to the lower levels of citrate carrier (CiC). We demonstrate that aged cells showed enhanced lysosomal degradation of CiC, which is mediated via mitochondrial-derived vesicles. Strikingly, restoring cytosolic acetyl-CoA levels either by exogenous CiC expression or via acetate supplementation, remodels the chromatin landscape and rescues the osteogenesis defects of aged mesenchymal stem cells. Collectively, our results establish a tight, age-dependent connection between mitochondrial quality control, chromatin and stem cell fate, which are linked together by CiC